Cured guayule rubber containing compositions and method for preparing same

ABSTRACT

Provided herein are cured rubber compositions containing guayule natural rubber with 2.5-4 weight % resin and fillers. By the use of a specified cure package that contains increased amounts of sulfur and accelerator, the cured rubber compositions are found to exhibit strain induced crystallization (as can be observed by X-ray diffraction). Also provided are related methods for preparing the rubber compositions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/894,278, filed Feb. 12, 2018, which is a continuation of U.S. patentapplication Ser. No. 13/787,644, filed Mar. 6, 2013, which issued onFeb. 13, 2018 under U.S. Pat. No. 9,890,268, which claims priority toand any other benefit of U.S. Provisional Patent Application Ser. No.61/607,494, filed Mar. 6, 2012, and entitled “CURED GUAYULE RUBBERCONTAINING COMPOSITIONS AND METHODS FOR PREPARING SAME,” the entiredisclosures of which are incorporated by reference herein.

BACKGROUND

Natural rubber sourced from the guayule shrub is well-known to contain asignificant amount of resin. The common understanding among thoseskilled in the art has been that the resin has detrimental effects onrubber compositions for use in tire-related components and to attempt toremove as much of the resin as possible.

SUMMARY

Provided herein are cured guayule-rubber containing compositions whichexhibit strain induced crystallization and methods for preparing thosecompositions. It was surprisingly found that cured rubber compositionscontaining guayule natural rubber with 2.5-4 weight % resin exhibitedstrain induced crystallization when the cure package was adjusted toincrease the amount of sulfur and accelerator but without any need toincrease the amount of stearic acid. This discovery was contrary toprevious teachings which were directed at removing as much resin aspossible from the guayule natural rubber (thereby increasing processingtime and cost in the guayule natural rubber production process) in anattempt to limit crack growth propagation in rubber compositionscontaining the guayule natural rubber. Because the raw plant matter fromthe guayule shrub can contain a considerable amount of resin that isdifficult to separate from the natural rubber also contained therein,the ability to use guayule natural rubber containing as much as 4 weight% resin has the potential to decrease processing complexity and costsassociated with isolation of natural rubber from the guayule shrub.

In a first embodiment is provided a cured rubber composition comprising:(a) 100 phr of guayule natural rubber, where the guayule natural rubbercontains 2.5-4 weight % resin and (b) 5-100 phr of at least one fillerselected from the group consisting of carbon black and silica. The curepackage used to prepare the cured rubber composition comprises: (i) 1.2to 4 phr sulfur, (ii) 0.5 to 5 phr of at least one antioxidant, (iii)0.5 to 5 phr zinc oxide, (iv) 0.5 to 4 phr stearic acid, (iv) 1.05 to 3phr of at least one accelerator and the cured rubber compositionexhibits strain induced crystallization (as can be observed by X-raydiffraction).

In a second embodiment is provided a cured rubber compositioncomprising: (a) 10-90 phr of guayule natural rubber, where the guayulenatural rubber contains 2.5-4 weight % resin, (b) 90-10 phr of at leastone conjugated diene monomer containing polymer or copolymer, and (c)5-100 phr of at least one filler selected from the group consisting ofcarbon black and silica. The cure package used to prepared the curedrubber composition comprises: (i) 1.2 to 4 phr sulfur, (ii) 0.5 to 5 phrof at least one antioxidant (standard), (iii) 0.5 to 5 phr zinc oxide,(iv) 0.5 to 4 phr stearic acid, (iv) 1.05 to 3 phr of at least oneaccelerator and the cured rubber composition exhibits strain inducedcrystallization as can be observed by X-ray diffraction.

In a third embodiment is provided a method of providing a cured guayulenatural rubber containing composition with strain inducedcrystallization. In the method, a rubber composition is utilized thatcontains (i) 100 phr of guayule natural rubber that contains 2.5-4weight % resin and (ii) 5-100 phr of at least one filler selected fromthe group consisting of carbon black and silica and a cure package isutilized that contains (i) 1.2 to 4 phr sulfur, (ii) 0.5 to 5 phr of atleast one antioxidant, (iii) 0.5 to 5 phr zinc oxide, (iv) 0.5 to 4 phrstearic acid, (iv) 1.05 to 3 phr of at least one accelerator to producea cured guayule natural rubber containing composition. The cured guayulenatural rubber containing composition exhibits strain inducedcrystallization (as evidenced by X-ray diffraction).

In a fourth embodiment is provided a method of providing a cured guayulenatural rubber containing composition with strain inducedcrystallization. In the method, a rubber composition is utilized thatcontains (i) 1-90 phr of guayule natural rubber that contains 2.5-4weight % resin, (ii) 90-10 phr of at least one conjugated diene monomercontaining polymer or copolymer, and (iii) 5-100 phr of at least onefiller selected from the group consisting of carbon black and silica anda cure package is utilized that contains (i) 1.2 to 4 phr sulfur, (ii)0.5 to 5 phr of at least one antioxidant, (iii) 0.5 to 5 phr zinc oxide,(iv) 0.5 to 4 phr stearic acid, (iv) 1.05 to 3 phr of at least oneaccelerator to produce a cured guayule natural rubber containingcomposition. The cured guayule natural rubber containing compositionexhibits strain induced crystallization (as evidenced by X-raydiffraction).

In a fifth embodiment is provided a method of providing a cured guayulenatural rubber containing composition with strain inducedcrystallization comprising: utilizing a rubber mixture comprising (i)100 phr of guayule natural rubber that contains 2.5-4 weight % resin and(ii) 5-100 phr of at least one filler selected from the group consistingof carbon black and silica, and curing the rubber mixture by increasingthe amount of sulfur in the cure package by 30-300% and increasing theamount of accelerator by 30-200% each as compared to a comparativerubber composition that contains Hevea natural rubber instead of guayulenatural rubber. The cured guayule natural rubber containing compositionand the comparative rubber composition both exhibit strain inducedcrystallization (as can be observed by X-ray diffraction) and have a maxstress at break, a 300% MPa and an elongation at break that are no morethan +/−15% different. The tan delta at 0° C. and 50° C. (obtained fromtemperature sweep experiments conducted with a frequency of 31.4 rad/secusing 0.5% strain for temperatures ranging from −100° C. to −10° C., andwith 2% strain for temperatures ranging from −10° C. to 100° C.) of thecured guayule natural rubber containing composition is no more than 5%different that the tan delta at 0° C. and 50° C. of the comparativerubber composition.

In a sixth embodiment is provided a method of providing a cured guayulenatural rubber containing composition with strain inducedcrystallization comprising: utilizing a rubber mixture comprising (i)1-90 phr of guayule natural rubber that contains 2.5-4 weight % resin,(ii) 90-10 phr of at least one conjugated diene monomer containingpolymer or copolymer, and (iii) 5-100 phr of at least one fillerselected from the group consisting of carbon black and silica, andcuring the rubber mixture by increasing the amount of sulfur in the curepackage by 30-300% and increasing the amount of accelerator by 30-200%each as compared to a comparative rubber composition that contains Heveanatural rubber instead of guayule natural rubber. The cured guayulenatural rubber containing composition and the comparative rubbercomposition both exhibit strain induced crystallization (as can beobserved by X-ray diffraction) and have a max stress at break, a 300%MPa and an elongation at break that are no more than +/−15% different.The tan delta at 0° C. and 50° C. (obtained from temperature sweepexperiments conducted with a frequency of 31.4 rad/sec using 0.5% strainfor temperatures ranging from −100° C. to −10° C., and with 2% strainfor temperatures ranging from −10° C. to 100° C.) of the cured guayulenatural rubber containing composition is no more than 5% different thatthe tan delta at 0° C. and 50° C. of the comparative rubber composition.

DESCRIPTION OF THE FIGURES

FIG. 1 is a graph showing tensile properties of rubber compositionscontaining Hevea natural rubber and varying amounts of guayule-sourcedresin at various elongations and at break.

FIG. 2 is a graph showing crosslink density of rubber compositions.

FIG. 3 is a graph showing tensile properties of rubber compositionscontaining either Hevea natural rubber with varying amounts of curativesor guayule natural rubber with varying amounts of resin at variouselongations and at break.

FIG. 4 is a graph showing crack growth resistance for rubbercompositions containing either Hevea natural rubber with varying amountsof curatives or guayule natural rubber with varying amounts of resin.

FIG. 5 shows the results of x-ray diffraction analysis of guayulenatural rubber containing compositions with either 1% or 2.5% resinversus Hevea natural rubber and is evidence of the presence of straininduced crystallization in the guayule natural rubber containingcompositions.

DETAILED DESCRIPTION

Provided herein are cured guayule-rubber containing compositions whichexhibit strain induced crystallization and methods for preparing thosecompositions.

Definitions

The terminology as set forth herein is for description of theembodiments only and should not be construed as limiting the inventionas a whole.

As used herein the term “resin” means the naturally occurring non-rubberchemical entities present in non-Hevea plants such as guayule shrubsmatter. These chemical entities include, but are not limited to, resins(such as terpenes), fatty acids, proteins, and inorganic materials, andinclude both polar and non-polar moieties.

Rubber Compositions and Methods

In a first embodiment is provided a cured rubber composition comprising:(a) 100 phr of guayule natural rubber, where the guayule natural rubbercontains 2.5-4 weight % resin and (b) 5-100 phr of at least one fillerselected from the group consisting of carbon black and silica. The curepackage used to prepare the cured rubber composition comprises: (i) 1.2to 4 phr sulfur, (ii) 0.5 to 5 phr of at least one antioxidant, (iii)0.5 to 5 phr zinc oxide, (iv) 0.5 to 4 phr stearic acid, (iv) 1.05 to 3phr of at least one accelerator and the cured rubber compositionexhibits strain induced crystallization (as can be observed by X-raydiffraction).

In a second embodiment is provided a cured rubber compositioncomprising: (a) 10-90 phr of guayule natural rubber, where the guayulenatural rubber contains 2.5-4 weight % resin, (b) 90-10 phr of at leastone conjugated diene monomer containing polymer or copolymer, and (c)5-100 phr of at least one filler selected from the group consisting ofcarbon black and silica. The cure package used to prepared the curedrubber composition comprises: (i) 1.2 to 4 phr sulfur, (ii) 0.5 to 5 phrof at least one antioxidant (standard), (iii) 0.5 to 5 phr zinc oxide,(iv) 0.5 to 4 phr stearic acid, (iv) 1.05 to 3 phr of at least oneaccelerator and the cured rubber composition exhibits strain inducedcrystallization as can be observed by X-ray diffraction.

In a third embodiment is provided a method of providing a cured guayulenatural rubber containing composition with strain inducedcrystallization. In the method, a rubber composition is utilized thatcontains (i) 100 phr of guayule natural rubber that contains 2.5-4weight % resin and (ii) 5-100 phr of at least one filler selected fromthe group consisting of carbon black and silica and a cure package isutilized that contains (i) 1.2 to 4 phr sulfur, (ii) 0.5 to 5 phr of atleast one antioxidant, (iii) 0.5 to 5 phr zinc oxide, (iv) 0.5 to 4 phrstearic acid, (iv) 1.05 to 3 phr of at least one accelerator to producea cured guayule natural rubber containing composition. The cured guayulenatural rubber containing composition exhibits strain inducedcrystallization (as evidenced by X-ray diffraction).

In a fourth embodiment is provided a method of providing a cured guayulenatural rubber containing composition with strain inducedcrystallization. In the method, a rubber composition is utilized thatcontains (i) 1-90 phr of guayule natural rubber that contains 2.5-4weight % resin, (ii) 90-10 phr of at least one conjugated diene monomercontaining polymer or copolymer, and (iii) 5-100 phr of at least onefiller selected from the group consisting of carbon black and silica anda cure package is utilized that contains (i) 1.2 to 4 phr sulfur, (ii)0.5 to 5 phr of at least one antioxidant, (iii) 0.5 to 5 phr zinc oxide,(iv) 0.5 to 4 phr stearic acid, (iv) 1.05 to 3 phr of at least oneaccelerator to produce a cured guayule natural rubber containingcomposition. The cured guayule natural rubber containing compositionexhibits strain induced crystallization (as evidenced by X-raydiffraction).

In a fifth embodiment is provided a method of providing a cured guayulenatural rubber containing composition with strain inducedcrystallization comprising: utilizing a rubber mixture comprising (i)100 phr of guayule natural rubber that contains 2.5-4 weight % resin and(ii) 5-100 phr of at least one filler selected from the group consistingof carbon black and silica, and curing the rubber mixture by increasingthe amount of sulfur in the cure package by 30-300% and increasing theamount of accelerator by 30-200% each as compared to a comparativerubber composition that contains Hevea natural rubber instead of guayulenatural rubber. The cured guayule natural rubber containing compositionand the comparative rubber composition both exhibit strain inducedcrystallization (as can be observed by X-ray diffraction) and have a maxstress at break, a 300% MPa and an elongation at break that are no morethan +/−15% different. The tan delta at 0° C. and 50° C. (obtained fromtemperature sweep experiments conducted with a frequency of 31.4 rad/secusing 0.5% strain for temperatures ranging from −100° C. to −10° C., andwith 2% strain for temperatures ranging from −10° C. to 100° C.) of thecured guayule natural rubber containing composition is no more than 5%different that the tan delta at 0° C. and 50° C. of the comparativerubber composition.

In a sixth embodiment is provided a method of providing a cured guayulenatural rubber containing composition with strain inducedcrystallization comprising: utilizing a rubber mixture comprising (i)1-90 phr of guayule natural rubber that contains 2.5-4 weight % resin,(ii) 90-10 phr of at least one conjugated diene monomer containingpolymer or copolymer, and (iii) 5-100 phr of at least one fillerselected from the group consisting of carbon black and silica, andcuring the rubber mixture by increasing the amount of sulfur in the curepackage by 30-300% and increasing the amount of accelerator by 30-200%each as compared to a comparative rubber composition that contains Heveanatural rubber instead of guayule natural rubber. The cured guayulenatural rubber containing composition and the comparative rubbercomposition both exhibit strain induced crystallization (as can beobserved by X-ray diffraction) and have a max stress at break, a 300%MPa and an elongation at break that are no more than +/−15% different.The tan delta at 0° C. and 50° C. (obtained from temperature sweepexperiments conducted with a frequency of 31.4 rad/sec using 0.5% strainfor temperatures ranging from −100° C. to −10° C., and with 2% strainfor temperatures ranging from −10° C. to 100° C.) of the cured guayulenatural rubber containing composition is no more than 5% different thatthe tan delta at 0° C. and 50° C. of the comparative rubber composition.

In certain embodiments according to the first and fourth embodimentsdescribed herein, the cured rubber composition has a max stress atbreak, a 300% MPa and an elongation at break that is no more than +/−15%as compared to a comparative rubber composition that contains Heveanatural rubber instead of guayule natural rubber. (The comparativerubber composition containing Hevea rubber has all other ingredients thesame as the composition containing guayule natural rubber but simplyreplaces the guayule natural rubber with the same amount of Heveanatural rubber. In addition, the methods used to mix the ingredients ofthe Hevea rubber composition and the guayule natural rubber compositionare the same.) In other embodiments according to the first and fourthembodiments described herein, the cured rubber composition has a maxstress at break, a 300% MPa and an elongation at break that is no morethan +/−10% as compared to a comparative rubber composition thatcontains Hevea natural rubber instead of guayule natural rubber. In yetother embodiments according to the first and fourth embodimentsdescribed herein, the cured rubber composition has a max stress atbreak, a 300% MPa and an elongation at break that is no more than +/−5%as compared to a comparative rubber composition that contains Heveanatural rubber instead of guayule natural rubber.

It is specifically contemplated that a tire component may be made fromany of the rubber formulations according to the first and fourthembodiments disclosed herein. Non-limiting examples of tire componentsthat may be made from the rubber formulations according to the first andfourth embodiments disclosed herein include treads, sidewalls and bodyskim plies.

In certain embodiments according to the second and fifth embodimentsdisclosed herein, the cured rubber composition has a max stress atbreak, a 300% MPa and an elongation at break that is no more than +/−15%as compared to a comparative rubber composition that contains Heveanatural rubber instead of guayule natural rubber. (The comparativerubber composition containing Hevea rubber has all other ingredients thesame as the composition containing guayule natural rubber but simplyreplaces the guayule natural rubber with the same amount of Heveanatural rubber. In addition, the methods used to mix the ingredients ofthe Hevea rubber composition and the guayule natural rubber compositionare the same.) In other embodiments according to the second and fifthembodiments described herein, the cured rubber composition has a maxstress at break, a 300% MPa and an elongation at break that is no morethan +/−10% as compared to a comparative rubber composition thatcontains Hevea natural rubber instead of guayule natural rubber. In yetother embodiments according to the second and fifth embodimentsdescribed herein, the cured rubber composition has a max stress atbreak, a 300% MPa and an elongation at break that is no more than +/−5%as compared to a comparative rubber composition that contains Heveanatural rubber instead of guayule natural rubber.

In certain embodiments according to the third and sixth embodimentsdisclosed herein, the cured rubber composition has a max stress atbreak, a 300% MPa and an elongation at break that is no more than +/−10%as compared to a comparative rubber composition that contains Heveanatural rubber instead of guayule natural rubber. In yet otherembodiments according to the third and sixth embodiments describedherein, the cured rubber composition has a max stress at break, a 300%MPa and an elongation at break that is no more than +/−5% as compared toa comparative rubber composition that contains Hevea natural rubberinstead of guayule natural rubber.

In certain embodiments according to the fourth, fifth and sixthembodiments disclosed herein, the at least one conjugated diene monomercontaining polymer or copolymer is selected from the group consisting of1,3-butadiene, styrene-butadiene copolymer and polyisoprene. In otherembodiments according to the third and sixth embodiments disclosedherein, the at least one conjugated diene monomer containing polymer orcopolymer contains at least one monomer selected from the groupconsisting of 1,3-butadiene, isoprene, 1,3-pentadiene, 1,3-hexadiene,2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene,2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene,4-methyl-1,3-pentadiene and 2,4-hexadiene; and optionally at least onemonomer selected from the group consisting of styrene, α-methyl styrene,p-methylstyrene, o-methylstyrene, p-butylstyrene and vinylnaphthalene.

In certain embodiments according to the first-sixth embodimentsdisclosed herein, the silica utilized (silicon dioxide) includeswet-process, hydrated silica produced by a chemical reaction in water,and precipitated as ultra-fine spherical particles. In certain of theforegoing embodiments, the silica has a surface area of about 32 toabout 400 m²/g, in another embodiment about 100 to about 250 m2/g, andin yet another embodiment, about 150 to about 220 m²/g. The pH of thesilica filler in certain of the foregoing embodiments is about 5.5 toabout 7 and in another embodiment about 5.5 to about 6.8. Commerciallyavailable silicas include Hi-Sil™ 215, Hi-Sil™ 233, Hi-Sil™ 255LD, andHi-Sil™ 190 (PPG Industries; Pittsburgh, Pa.), Zeosil™ 1165MP and175GRPlus (Rhodia), Vulkasil™ (Bary AG), Ultrasil™ VN2, VN3 (Degussa),and HuberSil™ 8745 (Huber).

In certain embodiments according to the first-sixth embodimentsdisclosed herein, the carbon black(s) utilized may include any of thecommonly available, commercially-produced carbon blacks. These includethose having a surface area (EMSA) of at least 20 m²/gram and in otherembodiments at least 35 m²/gram up to 200 m²/gram or higher. Surfacearea values include those determined by ASTM test D-1765 using thecetyltrimethyl-ammonium bromide (CTAB) technique. Among the usefulcarbon blacks are furnace black, channel blacks and lamp blacks. Morespecifically, examples of the carbon blacks include super abrasionfurnace (SAF) blacks, high abrasion furnace (HAF) blacks, fast extrusionfurnace (FEF) blacks, fine furnace (FF) blacks, intermediate superabrasion furnace (ISAF) blacks, semi-reinforcing furnace (SRF) blacks,medium processing channel blacks, hard processing channel blacks andconducting channel blacks. Other carbon blacks that may be utilizedinclude acetylene blacks. Mixtures of two or more of the above blackscan be used. Exemplary carbon blacks include those bearing ASTMdesignation (D-1765-82a) N-110, N-220, N-339, N-330, N-351, N-550, andN-660. In one or more embodiments, the carbon black may include oxidizedcarbon black.

In certain embodiments according to the first-sixth embodimentsdisclosed herein, other conventional rubber additives may also be addedto the rubber compositions. These include, for example, process oils,plasticizers, anti-degradants such as antioxidants and anti-ozonants,curing agents and the like.

Typically, process oils are added to tread rubber compositions as asoftener. Non-limiting examples of process oils used in the tread rubbercompositions disclosed herein include paraffinic, naphthenic, andaromatic process oils, and the like. In one or more embodimentsaccording to the first-sixth embodiments disclosed herein, the processoil is an aromatic process oil. In other embodiments, the process oil isa low polycyclic aromatic content (“low PCA”) oil containing less than2%. Other useful oils include those containing less than 3 wt %, lessthan 2 wt % or less than 1 wt % of polycyclic aromatic compounds (asmeasured by IP346) (“low PCA oils”). Such low PCA oils are increasinglyused in an effort to reduce the amount of polycyclic aromatic compoundspresent in rubbers used in tires. Commercially available low PCA oilsinclude various naphthenic oils, mild extraction solvates (MES) andtreated distillate aromatic extracts (TDAE).

In certain embodiments according to the first-sixth embodimentsdisclosed herein, where the rubber compositions are used for treads, therubber compositions preferably contain between 1 and 100 phr processoil. In one or more embodiments, the amount of process oil is between 2and 100 phr; in other embodiments, between 1 and 50 phr; in others,between 2 and 50 phr. In still other embodiments, the amount of processoil is between 1 and 20 phr; in others, between 2 and 20 phr; in others,between 1 and 10 phr; in still others, between 2 and 10 phr.

When forming a tread rubber composition, generally all ingredients maybe mixed with standard equipment such as, e.g., Banbury or Brabendermixers. Typically, mixing occurs in two or more stages. During the firststage (also known as the masterbatch stage), mixing typically is begunat temperatures of about 100° to about 130° C. and increases until aso-called drop temperature, typically about 165° C., is reached.

Where a rubber composition includes fillers other than (or in additionto) carbon black, a separate re-mill stage often is employed forseparate addition of the other fillers. This stage often is performed attemperatures similar to, although often slightly lower than, thoseemployed in the masterbatch stage, i.e., ramping from about 90° C. to adrop temperature of about 150° C. For purposes of this application, theterm “masterbatch” means the composition that is present during themasterbatch stage or the composition as it exists during any re-millstage, or both.

Curatives, accelerators, etc., are generally added at a final mixingstage. To avoid undesirable scorching and/or premature onset ofvulcanization, this mixing step often is done at lower temperatures,e.g., starting at about 60° to about 65° C. and not going higher thanabout 105° to about 110° C. For purposes of this application, the term“final batch” means the composition that is present during the finalmixing stage.

As previously discussed above, with respect to the first, second, fourthand fifth embodiments, the cured rubber composition or rubber mixtureutilizes a cure package comprising 1.2-4 phr sulfur, 0.5 to 5 phr of atleast one antioxidant, 0.5 to 5 phr of zinc oxide, 0.5-4 phr of stearicacid, and 1.05 to 3 phr of at least one accelerator. As also discussedabove, with respect to the third and sixth embodiments, the amount ofsulfur and accelerator in the cured guayule rubber containingcomposition is increased by 30-300% and 30-200% as compared to acomparative rubber composition that contains Hevea natural rubberinstead of guayule natural rubber, respectively, in order to compensatefor the resin content of the guayule natural rubber. As used herein, a100% increase should be understood to be a doubling in amount. Incertain embodiments of the third and sixth embodiments disclosed herein,the amount of sulfur in the cured guayule rubber composition isincreased by 30-200%. As a non-limiting example of the increased amountof sulfur and accelerator, if the amount of sulfur and accelerator inthe comparative rubber composition was 1.3 and 0.8, respectively, theamount of sulfur and accelerator in the guayule rubber containingcomposition could be 1.7-2.6 and 1.0-1.6, respectively.

Subsequently, the compounded mixture is processed (e.g., milled) intosheets prior to being formed into any of a variety of components andthen vulcanized, which typically occurs at about 5° to about 15° C.higher than the highest temperatures employed during the mixing stages,most commonly about 170° C.

EXAMPLES

The following examples are for purposes of illustration only and are notintended to limit the scope of the claims which are appended hereto.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the technology of this application belongs. While thepresent application has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Therefore, the application, in its broaderaspects, is not limited to the specific details, the representativeembodiments, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of the applicant's general inventive concept.

In order to investigate the effect of various resin levels on thephysical properties of cured guayule natural rubber containing rubbercompositions, rubber formulations containing 100 phr of guayule naturalrubber along with varying amounts of resin were prepared according tothe formulas provided below in Table 1. The resins that were added wereobtained from material that resulted from other work done on isolatingnatural rubber from guayule shrub using organic solvent based processes.This material represented the dried fraction (i.e., solvent removed) ofmaterial isolated in the polar organic solvent phase from the process.The amounts of resin added are weight % based upon the total weight ofthe natural rubber ((in other words, the stock indicated as containing1% resin utilized natural rubber that contained 1 weight % rubber sothat the rubber was 99 parts rubber and 1 part resin). The sameconvention is used in Table 2 below for the Yulex 1% and 2.5% rubbers.

TABLE 1 Ingredient/Amount (in phr) Stock A Stock B Stock C Stock D StockE Stock F Rubber 100 100 100 100 100 100 (#4RSS)¹ (Yulex)² (Yulex)(Yulex) (Yulex) (Yulex) Amount of resin 0 1.0 2.0 4.0 12.0 (weight %)Carbon black 50 50 50 50 50 50 Stearic acid 2 2 2 2 2 2 Antioxidant(6PPD) 1 1 1 1 1 1 Zinc oxide 3 3 3 3 3 3 Accelerator (TBBS)³ 0.8 0.80.8 0.72 0.64 0.56 Sulfur 1.3 1.3 1.3 1.17 1.04 0.91 ¹Hevea rubber inthe form of #4 rubber smoked sheet (RSS) ²Yulex guayule rubbercontaining approximately 1 weight % resin³2-(tert-butylaminothio)benzothiazole

After formulating, samples of each stock were subjected to testing todetermine the physical properties of the resulting stocks. Data obtainedis illustrated in FIGS. 1 and 2. As can be seen from FIGS. 1 and 2, thephysical properties of the rubber compositions generally decrease withan increasing amount of resin (compare stocks A and B to control stockC). FIG. 1 also shows that a rubber composition containing guayulenatural rubber with approximately 0% resin still shows lower modulus at300% than #4RSS. Notably, FIG. 1 also shows that the stock containingguayule rubber with approximately 0% resin is still lower than thoserubber compositions containing #4RSS. FIG. 2 shows cross link density ofthe guayule rubber containing compositions with 1% and 2.5% resin to beessentially equivalent.

In order to investigate the effect of the cure package components uponphysical rubber properties, rubber formulations containing 100 phr ofeither guayule natural rubber of Hevea natural rubber were preparedaccording to the formulas provided below in Table 2. As can be seen fromTable 2, the amount of sulfur and accelerator was adjusted inHevea-containing stocks D, E and F to be 90%, 80% and 70% of the amountin control stock C. Guayule natural rubber obtained from YulexCorporation was used in Stocks A and B.

TABLE 2 Ingredient/ Amount (in phr) Stock A Stock B Stock C Stock DStock E Stock F Rubber 100 100 100 100 100 100 (Yulex (Yulex (RSS)³(RSS)³ (RSS)³ (RSS)³ 2.5%)¹ 1.0%)² Carbon black 50 50 50 50 50 50Stearic acid 2 2 2 2 2 2 Antioxidant 1 1 1 1 1 1 (6PPD) Zinc oxide 3 3 33 3 3 Accelerator 0.8 0.8 0.8 0.72 0.64 0.56 (TBBS)⁴ Sulfur 1.3 1.3 1.31.17 1.04 0.91 ¹Yulex guayule rubber containing approximately 2.5 weight% resin ²Yulex guayule rubber containing approximately 1 weight % resin³Hevea rubber in the form of #4 rubber smoked sheet (RSS)⁴2-(tert-butylaminothio)benzothiazole

After formulating, samples of each stock were subjected to testing todetermine the physical properties of the resulting stocks. Data obtainedis reported in Table 3 below and illustrated in FIGS. 3 and 4. As can beseen from FIGS. 3 and 4, the physical properties of the rubbercompositions can be manipulated by adjusting the cure package to reducethe amount of sulfur and accelerator. Based upon the data obtained fromthe experiments done using varying amounts of resin content in guayulenatural rubber containing compositions and adjusting the cure package inHevea natural rubber containing compositions, it is postulated that thephysical properties of guayule natural rubber containing compositionscan be adjusted by changing the cure package to increase the amounts ofsulfur and accelerator by 30-300% and 30-200%, respectively, (as furtherdetailed herein, including in the claims).

TABLE 3 Yulex ~2.5% Yulex ~1.0% #4RSS #4RSS (w/ 90%) #4RSS (w/ 80%)#4RSS (w/ 70%) CMPD MOONEY (130° C., FINAL) MS1 + 4 (MU): 48.8 56.5 >20046.0 59.7 57.3 ML1 + 4 (MU): 47.0 59.5 MDR2000 (145° C., FINAL) ML (kg ·cm): 3.4 3.8 4.0 4.1 3.8 3.6 MN (kg · cm): 16.0 16.2 17.6 17.5 15.0 13.5MH − ML (kg · cm): 12.6 12.4 13.6 13.5 11.3 9.9 ts2 (min): 5.7 5.9 5.75.9 6.6 7.2 ts5 (min): 6.9 7.2 6.9 7.0 8.3 9.5 t50 (min): 7.5 7.7 7.77.8 8.7 9.4 t90 (min): 12.5 13.2 12.7 13.1 14.6 15.8 t100 (min): 23.724.4 22.5 22.8 24.8 26.7 MICRO DUMBELL TENSILE (23° C., FINAL, UNAGED)Max. Stress (MPa) 28.50 30.30 29.60 29.10 29.20 28.10 100% (MPa) 3.213.46 4.35 4.29 3.86 3.46 200% (MPa) 9.45 10.45 13.13 12.50 11.62 10.63300% (MPa) 16.89 18.79 23.00 21.48 20.20 18.91 Brk Strain % 474 457 380401 429 434 Toughness (MPa) 60.73 62.04 49.79 52.95 57.59 55.06 LAMBOURN(MULTI-PT, 65%) Avg. Wt. Loss: 0.1231 0.1214 0.1342 0.1284 0.1213 0.1172Avg. Intercept: 7.9433 8.0111 8.1611 8.1738 8.0729 8.0070 Avg. Slope:−0.0017 −0.0016 −0.0018 −0.0017 −0.0016 −0.0016 Avg. Correlation: −0.999−0.999 −0.999 −0.998 −0.999 −0.998

To the extent that the term “includes” or “including” is used in thespecification or the claims, it is intended to be inclusive in a mannersimilar to the term “comprising” as that term is interpreted whenemployed as a transitional word in a claim. Furthermore, to the extentthat the term “or” is employed (e.g., A or B) it is intended to mean “Aor B or both.” When the applicants intend to indicate “only A or B butnot both” then the term “only A or B but not both” will be employed.Thus, use of the term “or” herein is the inclusive, and not theexclusive use. See Bryan A. Garner, A Dictionary of Modern Legal Usage624 (2d. Ed. 1995). Also, to the extent that the terms “in” or “into”are used in the specification or the claims, it is intended toadditionally mean “on” or “onto.” Furthermore, to the extent the term“connect” is used in the specification or claims, it is intended to meannot only “directly connected to,” but also “indirectly connected to”such as connected through another component or components.

While the present application has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Therefore, the application, in its broaderaspects, is not limited to the specific details, the representativeapparatus, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of the applicant's general inventive concept.

What is claimed is:
 1. An improved tire rubber composition comprising acured mixture which comprises on a phr basis: a. 10-90 phr of guayulenatural rubber containing guayule resin and 90-10 phr of at least oneconjugated diene monomer containing polymer or copolymer, wherein thetotal amount of guayule natural rubber and conjugated diene monomercontaining polymer or copolymer is 100 phr, b. about 2 to about 4 phr ofguayule resin, c. about 50 to about 100 phr of at least one fillerincluding carbon black optionally in combination with silica, d. a curepackage comprising i. 1.7 to 4 phr of sulfur, ii. 0.5 to 5 phr of atleast one antioxidant, iii. 0.5 to 5 phr of zinc oxide, iv. 0.5 to 4 phrof stearic acid, and v. 2 to 3 phr of sulfur-containing accelerator,wherein (i) and (v) are present in a ratio of 0.75:1 to 2.6:1.
 2. Thetire rubber composition of claim 1, wherein the at least one conjugateddiene monomer containing polymer or copolymer includes styrene-butadienecopolymer.
 3. The tire rubber composition of claim 1, wherein the atleast one conjugated diene monomer containing polymer or copolymerincludes a monomer selected from the group consisting of 1,3-butadiene,isoprene, 1,3-pentadiene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene,2-ethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene,4-methyl-1,3-pentadiene and 2,4-hexadiene, and combinations thereof. 4.The tire rubber composition of claim 1, wherein the at least oneconjugated diene monomer containing polymer or copolymer is a polymerconsisting of 1,3-butadiene monomer.
 5. The tire rubber composition ofclaim 1, wherein the at least one conjugated diene monomer containingpolymer or copolymer includes a monomer selected from the groupconsisting of 1,3-butadiene, styrene, isoprene, and combinationsthereof.
 6. The tire rubber composition of claim 1, wherein the at leastone conjugated diene monomer containing polymer or copolymer furthercomprises a monomer selected from the group consisting of styrene,a-methyl styrene, p-methylstyrene, o-methylstyrene, p-butylstyrene andvinylnaphthalene, and combinations thereof.
 7. The tire rubbercomposition of claim 1, wherein the amount of sulfur is 1.7 to 2.6 phr.8. The tire rubber composition of claim 1, wherein (i) and (v) arepresent in a ratio of 1.1:1 to 2.6:1.
 9. The tire rubber composition ofclaim 1, wherein (i) and (v) are present in a ratio of 1.3:1 to 1.7:1.10. The tire rubber composition of claim 1, wherein (ii) is present inan amount of 0.5 to 3 phr and (iv) is present in an amount of 0.5 to 2phr.
 11. A tire tread comprising a cured mixture which comprises on aphr basis: a. 10-90 phr of guayule natural rubber containing guayuleresin and 90-10 phr of at least one conjugated diene monomer containingpolymer or copolymer, wherein the total amount of guayule natural rubberand conjugated diene monomer containing polymer or copolymer is 100 phr,b. about 2 to about 4 phr of guayule resin, c. about 50 to about 100 phrof at least one filler including carbon black optionally in combinationwith silica, d. a cure package comprising i. about 1.7 to about 4 phr ofsulfur, ii. about 0.5 to about 5 phr of at least one antioxidant, iii.about 0.5 to about 5 phr of zinc oxide, iv. about 0.5 to about 4 phr ofstearic acid, and v. about 2 to about 3 phr of sulfur-containingaccelerator, wherein the cured mixture exhibits strain inducedcrystallization as evidenced by X-ray diffraction and has at least oneof a max stress at break, a 200% Modulus, a 300% Modulus or anelongation at break that is no more than +/−15% as compared to acomparative rubber composition that contains Hevea natural rubberinstead of guayule natural rubber.
 12. The tire tread of claim 11,wherein the at least one conjugated diene monomer containing polymer orcopolymer includes styrene-butadiene copolymer.
 13. The tire tread ofclaim 11, wherein the at least one conjugated diene monomer containingpolymer or copolymer includes a monomer selected from the groupconsisting of 1,3-butadiene, isoprene, 1,3-pentadiene, 1,3-hexadiene,2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene,2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene,4-methyl-1,3-pentadiene and 2,4-hexadiene, and combinations thereof. 14.The tire tread of claim 11, wherein the at least one conjugated dienemonomer containing polymer or copolymer is a polymer consisting of1,3-butadiene monomer.
 15. The tire tread of claim 11, wherein the atleast one conjugated diene monomer containing polymer or copolymerincludes a monomer selected from the group consisting of 1,3-butadiene,styrene, isoprene, and combinations thereof.
 16. The tire tread of claim11, wherein the at least one conjugated diene monomer containing polymeror copolymer further comprises a monomer selected from the groupconsisting of styrene, a-methyl styrene, p-methylstyrene,o-methylstyrene, p-butylstyrene and vinylnaphthalene, and combinationsthereof.
 17. The tire tread of claim 11, wherein the amount of sulfur is1.7 to 2.6 phr.
 18. The tire tread of claim 11, wherein (i) and (v) arepresent in a ratio of 1.1:1 to 2.6:1.
 19. The tire tread of claim 11,wherein (ii) is present in an amount of 0.5 to 3 phr and (iv) is presentin an amount of 0.5 to 2 phr.
 20. A tire tread comprising a curedmixture which comprises on a phr basis: a. 10-90 phr of guayule naturalrubber containing guayule resin and 90-10 phr of at least one conjugateddiene monomer containing polymer or copolymer, wherein the total amountof guayule natural rubber and conjugated diene monomer containingpolymer or copolymer is 100 phr, b. about 2 to about 4 phr of guayuleresin, c. about 50 to about 100 phr of at least one filler includingcarbon black optionally in combination with silica, d. a cure packagecomprising i. about 1.2 to about 4 phr of sulfur, ii. about 0.5 to about5 phr of at least one antioxidant, iii. about 0.5 to about 5 phr of zincoxide, iv. about 0.5 to about 4 phr of stearic acid, and v. about 2 toabout 3 phr of sulfur-containing accelerator, wherein (i) and (v) arepresent in a ratio of 0.75:1 to 2.6:1, and wherein the cured mixtureexhibits strain induced crystallization as evidenced by X-raydiffraction and has at least one of a max stress at break, a 200%Modulus, a 300% Modulus or an elongation at break that is no more than+/−15% as compared to a comparative rubber composition that containsHevea natural rubber instead of guayule natural rubber.